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28 January 2011

Macular degeneration

Macular degeneration is a progressive eye condition in which the macula (the central part of the retina) is damaged, causing gradual loss of central, detailed vision.

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Summary

  • Macular degeneration is a progressive eye condition in which the part of the retina, called the macula, is damaged, resulting in lost central vision.
  • There are two main types of macular degeneration: “wet” macular degeneration and the more common “dry” macular degeneration.
  • Macular degeneration is most common among people of European descent over the age of 55.
  • The causes of macular degeneration are not completely understood, but there is a genetically inherited tendency, and smoking, dietary factors and sun exposure may play a role.
  • Macular degeneration is not curable, but the progress of the condition can be slowed in some people, if it is treated promptly.

Definition

Macular degeneration is a progressive eye condition in which the macula (the central part of the retina) is damaged, causing gradual loss of central, detailed vision. Central vision allows us to see the fine details when we look directly at something and is necessary for driving, reading, recognizing faces and doing close work such as sewing.

The retina is the light-sensitive membrane at the back of the eye which functions like the film in a camera. If the film is warped or damaged, it will not record the image that is “photographed by the eye”.

The macula degenerates as a result of aging. Small yellow or white deposits called “drusen” develop under the macula in normal eyes as they age. Drusen may lead to macular degeneration. Macular degeneration occurs when the retinal pigment epithelium, the insulating layer between the retina and the layer of blood vessels behind the retina (called the choroid) stops functioning efficiently. The macula may be damaged by blood vessels growing under the retina. The blood vessels may leak fluid or bleed (wet macular degeneration), or the retina may degenerate (dry macular degeneration).

Dry macular degeneration

This is the most common form of macular degeneration. When the eye is examined, the retina appears to have degenerated in certain areas and seems healthy in other areas. Damage to the macula is permanent, as it is not possible for it to grow back or heal. There are no eye drops, tablets, spectacles, operations or alternative therapies proven to restore the vision that has been lost. However, you will not go blind from this condition and will keep your peripheral vision. The disease is slowly progressive, and the rate of progress may be extremely slow. The condition eventually stabilises.

Wet macular degeneration

Wet macular degeneration is much less common. It is more rapidly progressive, but it also does not cause blindness, peripheral vision is preserved, and some people can be treated to preserve some useful vision.

It occurs when abnormal blood vessels develop under the retina and leak fluid, or bleed under the retina. The fluid, blood or vessels eventually disappear, but the central vision is permanently damaged, and a scar is formed.

Other macular diseases

There are macular diseases and degenerations that rarely occur in younger patients. Some of these conditions are genetic, while others can be caused by infections and inflammations or underlying conditions, such as diabetes.

Causes and risk factors

The causes of macular degeneration are not completely understood, but there is a genetically inherited tendency for the condition, and smoking, dietary factors and sun exposure over many years may play a role.

Macular degeneration is most common among people of European descent over the age of 55.

Symptoms and signs

Symptoms and signs include:

  • Blurred central vision – difficulty when reading and engaging in other activities that require good, fine eyesight
  • Lost central vision – dark or empty spaces
  • Distorted central vision – straight lines may appear wavy

Peripheral vision almost always remains normal, however.

Diagnosis

An ophthalmologist (eye specialist) will check your eyes and note the characteristic changes in the retina.

Monitoring

The ophthalmologist will see you for regular check-ups. You can also monitor your own condition using an Amsler Grid, which allows the patient or eye specialist to pick up subtle deterioration or changes in vision.

During this testing, you should wear the contact lenses or glasses you usually wear for reading. If you use bifocals, you should look through the reading portion of the lens.

Holding the grid at a comfortable reading distance (usually about 30 to 35 centimetres away), you should focus on the dot at the centre of the grid. Any wavy areas, blurred areas or blank spots observed should be marked on the grid, allowing for future monitoring of the progress of the condition.

Further (investigative) testing

If sight deterioration - monitored by daily use of the Amsler Grid – occurs or if the ophthalmologist notices any change, a fluorescein angiogram (or equivalent procedure) is performed to further assess the macula and to see if there is a treatable form of macular degeneration. If any change in the Amsler grid occurs, you should see your ophthalmologist immediately. Fluorescein angiography is a series of photographs taken after dye has been injected into a vein. The photographs will show the presence of abnormal fluid in the eye and changes in the condition of the retina, and exactly where these changes occurred. This will determine whether treatment is indicated.

Prevention

People who have a family history of macular degeneration, or who experience any vision problems should have regular eye exams after the age of 45. This will enable early diagnosis of the disease and make the few treatments that are available more effective.

Although macular degeneration cannot be prevented, you may be able to delay the onset or slow the progression by:

  • Not smoking cigarettes and avoiding cigarette smoke. Smoking is the most commonly identified factor that aggravates the condition.
  • Avoiding contact with ultra-violet light (UV rays) by wearing protective eye gear that blocks out 100% of UV rays.
  • Proper nutrition – particularly balanced and sufficient intake of vitamins, minerals and fresh vegetables – is also believed to help prevent the condition, and at the very least will improve general health.
  • Regular exercise, which improves both general and eye health.

Research into the genes that cause macular degeneration continues.

Treatment

There is currently no proven treatment for dry macular degeneration, however in some people with the condition, supplements containing vitamins, lutein or certain trace elements such as zinc or selenium may slow the progress of the disease. There are also many unproven treatments, on which desperate patients will spend as much as they can afford in an attempt to regain their vision. Unfortunately these therapies are unproven and usually benefit the therapist more than the patient.

If diagnosed early, wet macular degeneration can be treated in some patients by laser photocoagulation treatment. A newer variation of laser treatment is photodynamic therapy (PDT). In laser photocoagulation treatment, a laser is used to seal leaky blood vessels and inhibit their growth, thereby preventing further deterioration of eyesight.

A new injection is now being used to treat wet macular degeneration. A substance called Avastin or Lucentis that inhibits new blood vessel formation is injected into the vitreous humour of the eye. This helps to stop the leakage from the new blood vessels, which causes retinal damage. The main aim of the injection is to prevent further vision loss, but sometimes it actually improves central vision.

In the case of partial blindness caused by macular degeneration, “low vision rehabilitation” can help you adjust to your condition. Rehabilitation may include

  • adjusting the lighting in your home
  • visual aids and voice-activated devices
  • seeking assistance from someone with good eyesight to perform daily work and tasks

If you have incurable dry macular degeneration, your doctor or dietician may be able to recommend nutritional supplements, although the effect of these is not clinically proven.

Outcome of treatments

Laser photocoagulation treatment, even when successful, results in a scar and a permanent blind spot in the treated area. Vision will not normally improve, and sometimes is actually worse immediately after this treatment. However, if it halts the development of the disease in the treated areas, this therapy may result in less long-term vision loss than if no treatment were given. It may also reduce visual distortion. The earlier the condition is diagnosed, the more successful the therapy is in slowing the disease.

Low vision rehabilitation can allow macular degeneration sufferers with access to good public transport and assistance from family or friends to live fairly normal lives, even if they are partially blind.

There is extensive research into this condition, both locally in South Africa and internationally. Areas of research include genetics, new lasers, surgical techniques and medicines.

When to call the doctor

Consult your eye-care specialist without delay if you experience any symptoms of macular degeneration, and you should also be regularly tested to ensure that the problem is picked up sooner rather than later.

Also, consult your eye specialist before trying any treatment. This is  to ensure that any “miracle cures” on the market will, at least, not damage your health.

Reviewed by Dr L.C. Boezaart, M.B.Ch.B, M.Prax.Med, M.Med (Ophth).

Reviewed by Dr Clive Novis, Ophthalmologist (OSSA member), November 2010

 
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